Huge Planet Defies Explanation

by SPACE.com Staff | October 06, 2008 02:50pm ET

One of the densest exoplanet to date is a world known as COROT-exo-3b. It is about the size of Jupiter, but 20 times that planet’s mass, making it about twice as dense as lead. Scientists have not ruled out that the COROT-exo-3b may be a brown dwarf, or failed star. Credit: ESO/OAMP

Astronomers have sighted a very dense planet-sized object
that orbits its parent star in just four days and six hours.

The object, COROT-exo-3b, fits into the category of a
failed star known as a brown
dwarf, but the team that made the discovery has not ruled out the
possibility that it is a planet. Brown dwarfs are failed
stars. They burn lithium but are not massive enough to generate the
thermonuclear fusion of hydrogen and helium that powers real stars. Planets do
none of that.

"It has puzzled us; we?re not sure where to draw the
boundary between planets and brown dwarfs,? said Hans Deeg, an astronomer at
the Instituto de Astrofisica de Canarias (IAC) in the Canary Islands, Spain.

The object has a mass 20 times greater than that of
Jupiter, but is roughly the same size. It falls outside the range of planets
and stars discovered to date, with the largest planets having 12-Jupiter-mass
and the smallest stars 70-Jupiter-mass.

If astronomers confirm the object as a planet, it would
weigh in as the most massive and densest planet found
so far. A full study will be detailed in the journal Astronomy and
Astrophysics.

"COROT-exo-3b might turn out to be a rare object
found by sheer luck", said Francois Bouchy, an astronomer at the Institut
d'Astrophysique in Paris. "But it might just be a member of a new-found
family of very massive planets that encircle stars more massive than our sun.
We?re now beginning to think that the more massive the star, the more massive
the planet."

Ground-based telescopes around the world helped pinpoint
the object, including observatories in France, Chile, Germany, Hawaii, Israel
and Spain's Canary Islands.

The hunt for exoplanets has intensified over recent
years, with astronomers usually finding
such objects indirectly by observing their gravitational influence on
parent stars. Another team showcased what might be the first
direct image of an exoplanet around a sun-like star in September.